Biomedical Engineering – From Theory to Applications

An Ancient Model Organism to Test In Vivo Novel Functional Nanocrystals
Fig. 15. Methods used to evaluate the toxicity of CdTe-QDs on Hydra
Two different methods can be used to assess the toxicity of a given compound on Hydra. The
first method (used in A and B) is based on the evaluation of animal morphological traits,
while the second one (C) is based on survival rates. In A the time response toxicity curves to
equivalent TGA-QD concentrations are compared to the curves obtained by two different
concentrations of Cd salts. 25 Hydra were treated with the indicated compound and
morphological scores were monitored over 24, 48 and 72hr. In B the number of the animals
presenting different scores are reported for each time point in the three graphs (24, 48, 72hr).
The red arrows highlights that the score values decreasing from ten (untreated animals) to
zero obtained with 25nM concentration, after 72hr of incubation. In C the median lethal time
and median lethal concentration were calculated using the Sperman-Karber method.
In this way sub-lethal doses were determined and used for assessing the potential longterm
toxic effects induced by CdTe QDs on Hydra reproductive capabilities (Ambrosone et
al., 2011; Tino et al., 2011). Growth rate of Hydra tissue is regulated by the epithelial cell
cycle, which normal length (about 3 days) is controlled by environmental conditions, i.e.,
the feeding regime (Bosch and David, 1984). Thus, for a given feeding condition, the
growth rate is an indirect measure of the Hydra tissue growth and cell viability. The
number of individuals generated by an adult polyps over two-three weeks can be used to
calculate the growth rates constant (k), which is the slope of the regression line using the
standard equation of logarithmic growth: ln (n/n°) = kt (where n is the number of
individuals at the time t, and n° is the number of the founder polyps). Representative
growth rate curves determined for QD treated and untreated animals are shown in the
graph of Figure 15, and indicate k values lower for QD treated animals compared to
control. These differences were found significant by statistical analysis of repeated
experiments (Ambrosone et al, unpublished).
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